The present invention relates generally to aircraft protection and antidetection systems and more specifically the invention pertains to a plasma cloaking device which provides microwave absorption using a varying magnetic field.
Traditional aircraft antidetection systems are divided into two broad categories: active systems (which generate radar jamming signals); and passive systems, which rely on some characteristics of the vehicle to reduce the radar return. When the radar jamming transmitter is located on the target aircraft, the jamming signal transmitted by the aircraft can sometimes act as a beacon to the radar tracking system. Passive systems, which include the use of radar absorbing materials on the vehicle's surface, are limited in their ability to reduce the vehicle's radar cross section.
The task of providing a microwave absorption system which can reduce the detectability of satellites and aircraft, and which can protect targets from directed energy weapons is alleviated, to some extent, by the systems disclosed by the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 3,127,608, A. L. Eldridge, Object Camouflage Method and Apparatus;
U.S. Pat. No. 3,713,157, Henry August, Energy Absorption by a Radioisotope Produced Plasma;
U.S. Pat. No. 3,773,684, Alvin M. Marks, Dipolar Electro-Optic Compositions and Method of Preparation; and
U.S. Pat. No. 4,791,419, Gary R. Eubanks, Microwave Absorbing Means.
The August patent, Energy Absorption by a Radioisotope Produce Plasma, which describes a means of attenuating electromagnetic radiation passing through an ionized gas plasma adjacent to a body, teaches placing a radioisotope material on a surface of the body in contact with the gaseous medium surrounding the object. Such radioisotope material ejects energetic particles and quanta into the medium and causes ionization of the gas, forming an ionized gas plasma sheath around the object. This plasma sheath would absorb any electromagnetic energy entering it or would so distort any incoming signal that it would be unrecognized as a radar signal upon its return to its source. This patent also suggests superimposing a DC magnetic field upon the plasma in order to enhance attenuation.
The plasma around the object is constantly replaced by the continuous release of energetic particles and quanta into the gaseous medium surrounding the object. Additionally, this patent predicts a decrease in the plasma density as the distance from the object increases, providing impedance matching and a resulting decrease in the reflectivity of the plasma sheath.
The Eldridge Patent, Object Camouflage and Apparatus, teaches rendering an object invisible to radar by use of an ionized gas cloud surrounding the object. A particle accelerator is used to continuously ionize the gas immediately in front of the object and the object's forward progress through the ionized gas cloud provides the necessary coverage of the object. This patent teaches that the ionized gas cloud will attenuate and refract any incident electromagnetic waves, which effectively makes the object invisible to radar.
The Marks Patent, Dipolar Electro-optic Compositions and Method of Preparation, teaches using a suspension of dipolar particles as a light-controlling means. The particles are in suspension and are oriented by the application of an external electric or magnetic field. This patent teaches a method for creating such a device in which the particles are evenly distributed throughout the suspension, have a fast orientation response upon application of the appropriate exterior field, and are sufficiently transparent or reflective to electromagnetic radiation, depending upon orientation, to allow use of the device as a practical light-controlling device.
The Eubanks Patent, Microwave Absorbing Means, defines a device which is designed to absorb the microwave radiation used in traffic control radar by using a microwave antenna connected to a microwave absorbing means. This patent teaches winding a wire around a fluorescent light bulb as a helical microwave antenna. Each end of the antenna is then electrically coupled to the absorbing tube (fluorescent light bulb) so that the microwave radiation received by the antenna is transmitted to the absorbing tube where it is then absorbed by the gas contained within the tube.
While the above-cited references are instructive, they do not acknowledge that a varying magnetic field in proximity with a plasma produces dramatic microwave absorption. More specifically, microwave absorption is enhanced when the varying magnetic field is produced near electron cycloton resonance.
The August reference discussed above teaches the use of a plasma to attenuate radar signals and suggests superimposing a DC magnetic field on the plasma as a means of enhancing attenuation. The Eldridge reference teaches using an ionized gas cloud to cloak an object, but fails to disclose or predict the use of a magnetic field with the ionized gas cloud to increase attenuation of the incident radar signals.
The Eubanks reference teaches the absorption of radar signals so as to reduce or negate any reflected signal, but this reference neither claims nor predicts the use of a dipolar magnetic field supplied with a weak plasma to absorb incoming radar signals. There are no plasmas in this reference.
The Marks reference is not concerned with the absorption of radar signals at all, but is a light-controlling device. There is no plasma present in this reference and a magnetic field, if present, is used for the sole purpose of controlling the orientation of dipolar particles in suspension.
While the above-cited references are instructive, there remains the need to provide a system capable of cloaking a target using a dipolar magnetic field supplied with a weak plasma to absorb probing radar signals. The present invention is intended to satisfy that need.